HW zone on steam questions

Frank Dobbs

I have a townhouse in NYC.

Steam boiler is oversized Weil-McLain EG-75, 240k BTU/hr. 4 years old.

There was a separate steam system for the 1st floor until 2002 because it was a restaurant. They had a heat exhchanger/forced air system, which I removed when I added the space to the residential upstairs. There is now no heat on the 1st floor.

Needless to say, the system is short-cycling like crazy.

I am about to install a HW zone for the 1st floor and bsmt. I have paid for nice looking hydronic radiators that will arrive from Italy any day through Pronto/heating depot.

I sent my plumber Dan Holohan's excellent FAQ on condensate HW heating. He is willing to follow it and save the cost of a heat exchanger.

My plumber's question:
"The question I have is, does the piping to the radiation have to be 3/4" in order for the pressure thing to work going up to the first floor. Pronto says it needs to be 1". Maybe you could e-mail that heating site and see what they have to say about pipe size on a non heat exchanger system. It would reduce your cost to do it this way but you might have to re-pressurize the system once in a while from air getting in."

From reading the FAQ, it seems clear to me that there is no necessary size, but that the pipe size only determines the maximum BTU output.

My question:
Reading Dan's FAQ, I am afraid this whole approach may be misconceived. He says not to oversize the boiler in order to run HW zone. If that is true, the HW zone will not help the fact that the boiler is currently oversized.

I was hoping that some combination of a HW heating zone, a big domestic HW takeoff and downfiring the boiler somewhat would solve the oversizing problem. But if the fact is that the sizing should only be determined by the steam heating load, then my situation is hopeless.

The plumber has not been able to get the supply shop to do a radiation count in the existing steam system. But a heat loss analysis comes out to about 57,000 BTU's. I have Danfoss thermostatic valves, but how much radiation could I have. On 0 degree days, my radiation is adequate, but not execessive.

Also, as part of installling the HW system downstairs, we will remove about 35' of steam line and 35' of return in the basement. This will reduce the iron steam load even further.

Is it possible that all the heating specialists I have spoken to and a respected supply house are fundamentally in error?